The present invention relates to an image forming method for controlling the transfer of an image to a paper sheet, the separation of the paper sheet, and the transport of the paper sheet. More particularly, the present invention is concerned with an image forming method for determining an image transfer condition, a paper separation condition, a paper transport condition and conditions auxiliary thereto as well as a toner image forming condition on a photoconductive element by estimating each of a transfer state, a separation state and a transport state as a combination of membership functions of various kinds of information.
An image forming apparatus capable of controlling image transfer, paper separation and paper transport is disclosed in, for example, Japanese Patent Laid-Open Publication No. 125074/1983. The apparatus disclosed in this reference includes a humidity sensor responsive to humidity inside of the apparatus, and paper transporting means having a heater for dehumidifying a recording medium, i.e., a paper sheet. The paper transporting means is controlled on the basis of the output of the humidity sensor to adjust a paper transport speed, whereby a paper sheet is constantly held in a desirable state for high image quality. On the other hand, Japanese Patent Laid-Open Publication No. 64270/1982 teaches an electrostatic copying method which measures the thickness and specific resistance of a paper sheet during the interval between the feed of the paper and the image transfer, performs calculations with the measured values, and controls various conditions relating to image transfer and paper separation in matching relation to the results of calculations. This kind of method is contemplated to promote smooth paper separation with no regard to the kind of the paper sheet and environmental conditions, thereby preventing the image quality from being degraded in the image transferring and paper separating steps.
However, the above-described conventional schemes each determines an image transfer condition, a paper separation condition and a paper transport condition on the basis of only independent control information, e.g., the output of the humidity sensor (Lai-Open Publication No. 125074/1983) or the thickness and specific resistance of a paper sheet (Laid-Open No. 64270/1982). Stated another way, the conventional schemes simply set image transfer, paper separation and paper transport conditions as fixed values or as adequate values associated with a typical situation and do not totally determine a complicated correlation of electric and physical characteristics, environmental information, time information, etc. Specifically, even when the state of a paper sheet that effects the image transfer and paper separation and transport is changed, the conventional approaches simply set up conditions which prevent the image quality from being noticeably degraded or, if the image quality is slightly degraded, eliminates a paper jam or similar fault which affects the entire system. Consequently, the set conditions are simply standard ones which are not causative of noticeable faults, i.e., not optimal ones each matching a particular situation. It follows that optimal values of image transfer, paper separation and paper transport conditions as well as conditions auxiliary thereto cannot be computed, preventing a stable attractive image from being produced at all times.
Generally, regarding the relation between the characteristics of paper and the transfer, separation and transport characteristic, thin paper or similar extremely pliant paper is not easily separable while color paper and paper whose electric resistance has been lowered due to, for example, moisture are inferior in transferability than the others. Further, bond paper or similar rough paper has poor transferability. On the other hand, a paper sheet which does not have a toner image at a leading edge portion thereof is not readily separable, and a dot image, line image or similar halftone image is degraded when the transfer condition is excessive. In addition, since an image transferring device and a paper separating device deteriorate due to aging, the transfer, separation and transport abilities cannot be maintained constant unless the various conditions are changed.